The present embodiments relate to a power amplifier device for a magnetic resonance device.
Power amplifier devices are already in use in magnetic resonance devices of the prior art, since as part of the imaging process, nuclear spins, oriented via a transmit antenna, of an examination object are to be excited. High levels of power are used to operate this transmit antenna. The high levels of power are provided by a power amplifier device that may be incorporated into a transmit unit of the magnetic resonance device.
Known power amplifier devices frequently work with at least one power amplifier module, which has at least one power electronics component. As many components and/or conductive patterns as possible may be implemented on a common circuit board. Power amplifier devices that have several amplifier modules (e.g., four amplifier modules) each generating an output power of 5 to 8 kW, so that in combination a power of, for example, 30 kW may be achieved, are known. The power amplifier modules, which represent an output stage, may therefore also be referred to as output stage modules. Push-pull output stages that work on the push-pull principle with symmetrical input signals may be used. Because of the high level of power to be generated with the power amplifier device, the transistors used in the power amplifier modules as power electronics components are cooled. It is known to arrange a cooling plate (e.g., made of copper) underneath the circuit board (e.g., a printed circuit board (PCB)), through which cooling plate coolant channels, draining positions to be cooled, are routed.
In this connection, electronics structures (e.g., conductive patterns) that fulfill their function thanks to the interaction between conductor paths that are arranged on opposing sides of the circuit board may also be used. In the example of the amplifier modules, which work in push-pull mode (e.g., as a push-pull output stage), in each case a phase of a symmetrical input signal is assigned to a same number of transistors. This provides that a first group of transistors (e.g., including just one transistor) receives a 0° signal, while the other group of transistors (e.g., including just one transistor) receives a reversed-phase 180° signal. The drain outputs of the transistor components are combined in a first conductor path, which is in inductive exchange with the second conductor path, so that thanks to inductive coupling, the amplified output signal may be generated. An example of such electronics structures based on inductive (e.g., based on a magnetic field) coupling is a balun, where such electronics structures may also be used for generating the input signals for the transistor components.
Examples of such known power amplifier units may be found in DE 10 2011 006 061 A1 or DE 10 2011 088 028 A1.
A particular problem is the implementation of the electronics structures, in which conductor paths arranged on two opposing sides of the circuit board are to interact with one another. Whereas such electronics structures may be implemented externally to the circuit board using coaxial cable or the like, significant cable lengths, for which there is not enough space, may be used. For the correct, desired coupling of the conductor paths, a free space filled with air or a material with a dielectric constant close to that of air is to be provided. This is not possible if the metal of a cooling plate directly abuts a side of the circuit board. Hence, in the prior art, extremely complex implementations, which, for example, work using ferrites or divided cooling plates that are mechanically difficult to manipulate, may be pursued. For example, the free space provided for the inductive or magnetic interaction between the conductor paths is enclosed by grounded conductive material. For this reason, for a suboptimal, complex and difficult manufacturing process, circuit boards may be bonded to the cooling plates.